The present invention relates to weigh scales, and more particularly to body weigh scales.
Scales are devices that are used to determine the weight of an object by measuring the gravitational pull exerted on that object. Scales are commonly used to determine the physical amount or quantity of an item, such as a foodstuff, for example.
Body weigh scales can be found in many contemporary homes, usually in a bathroom. For this reason, the body weigh scales are often called xe2x80x9cbathroom scales.xe2x80x9d In general, body weigh scales include a platform onto which a user steps, and the user""s weight is then displayed. Body weigh scales allow a user to monitor his or her weight, usually before or after a shower, or just after waking up in the morning.
Many body weigh scales are mechanical, spring scales. In a spring scale, a platform is connected to a spring, which either stretches or compresses to balance a load (i.e., a person) placed on the platform. A needle, whose position depends on the extent to which the spring is stretched or compressed, indicates the weight of the load. Some mechanical scales include a pulse counter and a digital display upon which the user""s weight is shown.
Electronic body weigh scales utilize electricity to measure loads. Electronic scales are faster, and generally more accurate, than their mechanical counterparts. A common type of electronic scale uses a strain-gauge load cell. This type of scale has a platform supported by a column, with a strain gauge or gauges fused to the column. A strain gauge is a thin wire whose electrical resistance changes when the wire is stretched or compressed. When a load is placed on the platform, the column and strain gauge are compressed. The corresponding change in resistance of the strain gauge can be used to determine the person""s weight. The column of the strain-gauge load cell must be mounted in a rigid structure that does not deflect under the load on the body weigh scale. Otherwise, some of the strain of the object being weighed may be released as strain in the structure. By using a rigid structure, the weight of the object being weighed (e.g., a person) is transferred directly to the strain-gage load cell or cells, so that the column may fully compress relative to the rigid structure and the strain gages in the load cell may provide accurate information about the weight on the body weigh scale.
Although strain-gauge load cell scales work well for their intended purpose, there is a problem with their manufacture. For many contemporary strain-gauge load cell scales, it is desirable that the upper surface, or load-receiving platform, be decorative, such as a glass top, a faux marble top, a natural material such as stone or marble, or similar decorative surfaces formed from a plastic material. For glass load-receiving platforms, it has not been possible to form the load-receiving platform integral with the structure for receiving the column of the strain-gauge load cell, because glass does not allow much flexibility in shape-forming in its manufacture. Thus, the structure for receiving the column of the strain-gauge load cell is typically provided in a base that is separate from the load-receiving platform and that is connected, for example by gluing, to the load-receiving platform. An example of a scale having a separate base and load-receiving platform structure is shown in U.S. Pat. No. 5,955,705 to Germanton. That patent shows a load-receiving platform that fits over a U-shaped frame or base.
Another reason for using the two-piece, load-supporting platform and base construction is that the wires and related circuitry for the strain gage load sensor are typically sandwiched between the load-supporting structure and the base. Without the space between these two members, a structure is not available for containing the wires.
The use of natural materials, such as stone, marble, or the like, is expensive on a material basis and a manufacturing basis. Often, to achieve the desired shape, the load-receiving platform must be ground, polished, and/or cut. After the load-receiving platform is formed, it still has to be attached to a base that includes the strain-gauge load cells, because producing the structure for supporting the strain-gauge load cells from the natural material would be difficult and expensive.
For load-receiving platforms that are made of decorative plastic surfaces, it has not been possible to form the structure for receiving the strain-gauge load cell integral with the load-receiving platform, because the plastic materials having the faux finishes are not substantially rigid, and typically, because of shrinkage problems, do not maintain the desired decorative finish upon cooling of the parts. Most of the body weigh scales that include plastic materials with a faux finish are compression molded. Because of uneven height shrink rates in compression molding, to have an ideal decorative surface, most plastic materials must be produced as flat pieces, or otherwise there may be color distortion, surface sinks, visual level changes, or warpage. For this reason, it is difficult to compression mold a scale in one piece that includes a structure for receiving the strain-gauge load cell and that has an attractive decorative surface. If injection molding or die casting is used, the load-receiving platform may experience creepage or age deformation.
Moreover, the plastic material used to create the faux finishes is typically not rigid enough to provide the support for the strain-gauge load cell, unless it is provided at very large thicknesses. If the strain-gage load cells and related circuitry are mounted underneath the load-receiving platform, the scale must be even taller to receive these structures. Even if it were possible to fabricate the structure for receiving the strain-gauge load cell integral with the load-receiving platform, the resulting structure would have to be extremely thick to have the necessary rigidity for use with strain-gauge load cells. Recessing the strain-gage load cells in the load-receiving platform is not practical, because doing so creates thinned areas in the load-receiving platform, which further weakens the load-receiving platform (i.e., makes it less rigid), which may result in adverse effects to the finish of the scale. To avoid these problems, as with the scales having glass load-receiving platforms, the scales using decorative plastic for the load-receiving platform typically utilize a separate load-receiving platform that is mounted over a rigid base that houses the strain-gage load cells and related circuitry.
The two-piece construction of a base and a load-receiving platform in contemporary scales results in high costs for assembly. In addition, the resulting scale is an assembled product that is generally at least 1xc2xd inches high, which may be considered larger and more bulky than desired for some uses.
The present invention is directed to a body weigh scale that is formed of a polymeric, decorative material that is sufficiently rigid so that it may be produced relatively thin, and yet not significantly deflect under load. Moreover, the polymeric, decorative material provides an attractive surface after molding. To this end, the body weigh scale incorporates a fiber-filled, polyester thermosetting polymer material that has extremely low shrinkage rates so that the outer pattern and shape of the scale is not affected by the forming of very thin cross sections adjacent to thick cross-sections. This feature permits the scales to be formed with integral recesses for housing strain gages. In addition, the fiber-filled, polyester thermosetting polymer material is sufficiently rigid to permit a body weigh scale to be constructed having a low profile and having a load-receiving platform with integrally-formed strain-gauge load cell receptacles. The rigidity of the fiber-filled, polyester thermosetting polymer material provides sufficient structural support for operation of the strain-gauge load cells with a thin platform and without significant deflection of the material.
The body weigh scale may be formed from the fiber-filled, polyester thermoset material using a variety of thermosetting polymer formation methods. As examples, the body weigh scale may be formed using compression, transfer, or stuffer injection molding. Injection molding may be performed using a reverse inverted temperature process, which involves cold barrel injecting into a hot mold.
By using the fiber-filled, polyester thermosetting polymer material, there is significant molding flexibility for the load-receiving platform of the body weigh scale. For example, ribs may be formed integral with the load-receiving platform for receiving the wiring for the strain-gage load cells, without weakening the structure or causing color distortion, surface sinks, visual level changes, or warpage. In addition, a pocket may be formed in the top surface of the load-receiving platform for receiving a digital display, such as a light emitting diode (LED) display or a liquid crystal display (LCD).
The strength of the fiber-filled, polyester thermosetting polymer material permits the body weigh scale to have a profile that is thin as 0.302 inches for a 330 pound scale, and as thin as 0.380 inches for a 500 pound scale. This allows the body weigh scale to be lightweight and easily storable. In addition, the low profile of the body weigh scale provides a sleek look that matches many contemporary bathroom designs. Also, because the fiber-filled, polyester thermosetting polymer material has a low shrink rate, an aesthetically-pleasing decorative surface may be provided.
Other advantages will become apparent from the following detailed description when taken in conjunction with the drawings, in which: